Root canal therapy may involve the injection of a root canal filling material into the teeth cavities by means of a so-called pressure syringe which forces the filling material into said cavities. Other methods involve placement of solid gutta-percha and/or silver points coated with cement for filling the cavities, but these materials are difficult to apply and they do not completely penetrate into the fine crevices in the teeth cavities and, therefore, they frequently give poor filling performance. A more effective root canal filling material is described in U.S. Pat. No. 3,925,895 which issued on Dec. 16, 1975 and which is assigned to the assignee of the present application. The root canal therapy disclosed in said patent contemplates the injection into the tooth cavity of a hydrophyllic monomer (e.g., hydroxyethyl methacrylate) together with a suitable catalyst and an accelerator, and the in situ polymerization of said monomer in the tooth cavity. The monomer, catalyst and accelerator are mixed in a syringe to at least a paste-like consistency and then forced from the syringe into the root canal.
The root canal filling material described in said patent is more effective than the conventional root canal materials since it becomes hydrated and swells, thus filling and sealing the entire voids and crevices in the root canal.
A pressure syringe is available for root canal work which is not entirely satisfactory for injection of root canal filling materials such as the materials described in the aforementioned patent. Leakage of the material, inadequate obturation of the canal and loss of the filling material are but few of the disadvantages of the pressure syringe. Such pressure syringes are described by M. Greinberg in "Filling Root Canals of Deciduous Teeth by an Injection Technique," Dent. Digest 67: 574(December 1961) and in "Filling Root Canals by an Injection Technique," Dent. Digest 69: 61(February 1963). Accordingly, there is a need for a syringe which is suitable for the injection of root canal filling material of the type described in the aforementioned patent without the disadvantages and limitations which are inherent in the present pressure syringe system.